Reduced Live Load Feature

A new feature has been added to Online Plus in version 27 for loading agricultural trusses called Reduced Live Load. According to the IBC 2006 and 2009 editions, Table 1607.1 indicates that the minimum uniform roof live load for ordinary flat and pitched roofs is 20 psf.   However, section 1607.11.2 of the code also permits these types of roofs to have reduced roof live load based on the pitch and tributary area of the supporting trusses. It is important to note that the applicability of the minimum reduced roof live load be verified by the authority having jurisdiction and or by the building designer for the truss designs in question. 

With this new feature, if you check the box for reduced live load, the software will automatically calculate the reduced top chord live load based on the pitch, span and on center spacing of the trusses. This feature is enabled for a job by selecting “Edit / Job Properties Page / Uniform load tab” and checking “Reduced Live Load”.                                                                 



This feature can also be enabled for individual trusses by selecting the “UNI” icon (Change uniform loading for selected load case) and checking “Reduced Live Load”.   

A note will be placed on both the Portrait and Landscape Engineering drawings indicating the Reduced Live Load was used.   

There are certain restrictions for using the reduced roof live load feature.  You must be in an area where snow load is not controlling. The top chord uniform live load must be 20 psf and cannot be used in conjunction with the auto-snow load feature in the software.  The auto-snow load tool already uses snow load reductions based on ASCE 7 snow load criteria.

In version 27, only trusses with two symmetrical top chord pitches will be allowed to have the roof live load reduced. In upcoming versions, this may be expanded to include multiple pitches.



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